When comparing simulation results with observations, it is important to pay attention to the way quantities are evaluated in simulations. In particular,
estimates of metallicity (as well as other thermal properties) can be derived in different ways depending on the weight \(w\)  used to compute the average \(Z\)  value, that is \(Z_w = \int w Z {\rm d}V/\int w {\rm d}V\) . Typical weights are the mass of the gas or its emissivity in the X-ray band.
In general, flatter metallicity profiles in simulations are better reproduced when a projected emission-weighted estimate is pursued, whereas the mass-weighted three-dimensional metallicity typically shows a somewhat steeper decrease with radius [1]}.
In this perspective, the issue of a fair comparison between gas properties in simulations and observations has also been tackled via the generation of detailed X-ray synthetic observations out of numerical simulations, properly taking into account the specific characteristics of X-ray telescopes.
With such techniques, [2]} showed that an observational-like reconstruction of the iron and oxygen abundances with mock XMM-Newton observations of simulated clusters and groups is in good agreement with the intrinsic simulation value.
More recently, [3]} employed synthetic observations of the X-ray Integral Field Unit (X-IFU) on board the next-generation European X-ray observatory Athena to reconstruct chemical properties of the ICM from simulated galaxy clusters. The authors showed that the metallicity values obtained from X-IFU spectra match well the emission-measure-estimate computed directly from the simulations.
